1. The Field of the Invention
The invention generally relates to equipment for testing fiber-optic components. More specifically, the invention relates to gauging optical return loss in fiber-optic components.
2. Description of the Related Art
Fiber-optic networking can be used to communicate in modern high-speed networks. To transmit data on a fiber-optic network, the data must be converted from an electronic signal to an optical signal. This conversion may be done for example by using a transmitting optical subassembly (TOSA). The TOSA often includes a light generating device such as a laser or light emitting diode (LED). The light generating device is modulated according to the digital data to produce a modulated optical signal.
When optical signals are received, those optical signals must generally be converted to an electronic signal. This is often accomplished using a receiver optical subassembly (ROSA). A ROSA generally includes a photo sensitive device such as a photodiode connected to a transimpedance amplifier (TIA). When an optical signal impinges the photo sensitive device, a modulated current is induced in the photo sensitive device. This current can be converted by the TIA to an electronic signal usable by digital devices on a network.
Manufacturers of ROSAs and TOSAs typically perform various performance testing on the ROSAs and TOSAs before they are delivered to distributors and end customers. This performance testing can be used to detect defects or to sort components into groups of different rated values. More particularly, testing directed towards the ROSA may include testing the responsivity of the ROSA to a modulated optical signal, testing the amount of current produced for a given amount of optical signal and so forth. The ROSA may also be tested to determine a parameter known as optical return loss. Optical return loss is a measurement of the amount of optical signal that is reflected off of the face of the ROSA when an optical signal impinges the ROSA. This reflected light may cause unwanted reflections and interference in an optical network. Further, reflected light reduces the amount of power available for converting the optical signal to an electronic signal.
Different testing conditions may be needed to test different characteristics of the ROSA. For example, when testing the ROSA for responsivity or to measure current verses optical signal received, it is often desirable to use a low power optical signal so as not to trigger the automatic gain control circuitry in the TIA. However, when testing for optical return loss it is desirable to use a higher power optical source. Optical return loss may be as low as −12 dB. Therefore, if a low-power optical signal is used to test for optical return loss, the reflected optical signal may be insufficient to perform an accurate measurement. Maintaining different testing configurations for testing a ROSA may be relatively time-consuming. For example, testing a ROSA can include installing the ROSA in various test jigs to characterize the operating characteristics of the ROSA.